Certification standards of Underwriters Laboratories Inc. (UL) require that a recessed lighting fixture be designed and constructed to allow room-side access to the junction box where the branch circuit connections to the lighting fixture are made as well as access to any associated electrical component (transformer, ballast, driver, etc.). Access must be through an opening not less than six inches across. UL standards also require that the junction box be integral to the lighting fixture or securely fastened to its enclosure or frame. If the junction box is attached by a flexible conduit, it must have “additional means of securement.”
Many recessed lighting fixtures have their associated junction boxes and other components (transformer, ballast, driver, etc.) disposed laterally of the housing that contains the lamp assembly. In a traditional arrangement for lighting fixtures having an aperture of six inches or larger, the lamp housing, the junction box and other components are supported on a common pan or frame, which is secured to the adjacent building structure (joists, ceiling grid, etc.). A releasable connection between the lamp housing and the pan or frame allows the lamp housing to be dislodged and withdrawn from the ceiling opening to permit access to the nearby junction box and other components. In another common arrangement, often used in retrofit applications or other situations where the entire lighting fixture is to be supported only by an existing ceiling, the junction box and other components are supported on a laterally extending strut or arm attached to the lamp housing, usually forming a generally L-shaped unit. The lighting fixture is installed from below the ceiling through a ceiling opening that closely surrounds the lower end of the lamp housing when fully seated. The lighting fixture is removable through the same opening for servicing and access to the junction box. The size of the ceiling opening dictates the maximum size of the junction box and any other lighting fixture component, which must fit through the opening during installation and also during removal for servicing.
Many L-shaped retrofit assemblies can be somewhat difficult to install and remove, especially in situations where joist spacing is tight or where obstructions such as joist blocking, ductwork or piping are located close to the lighting fixture installation hole. Further, the small installation holes (e.g., 2⅞ inch or smaller) required for small aperture lamp housings make junction box miniaturization challenging, especially where the junction box must house a transformer, driver or other component. When above-ceiling access is available from the room through a properly sized auxiliary opening, a standard junction box can be used. Otherwise the usual solution is to mount the transformer or driver in an accessible remote location, which requires additional labor and materials.